A pressurized gas may be stored in a cylinder having an outlet valve. The valve can be opened manually to release the stored gas to exit the cylinder at flow rates that correspond to the storage pressure in the cylinder. For example, pressurized oxygen for home health care may be stored in an aluminum cylinder having such an outlet valve. When the oxygen is to be released from the cylinder, a pressure-reducing regulator is first mounted on the outlet valve so that the oxygen must pass through the regulator before it is accessible for breathing. The operator then opens the outlet valve on the cylinder, and the oxygen emerges from the regulator at a pressure that is greatly reduced from the storage pressure in the cylinder.
The regulator has a high pressure gas flow passage which receives the oxygen directly from the outlet valve on the cylinder. The high pressure passage conveys the oxygen to a spring-biased piston which operates to limit the pressure of the oxygen emerging from the regulator. Before the oxygen reaches the piston, it flows through portions of the high pressure passage that constrict toward a control orifice. Accordingly, the oxygen flowing through the regulator undergoes at least partially isothermal compression in the high pressure passage. A corresponding amount of heat is then absorbed and disipated by the structure of the regulator. For this reason known regulators are formed predominately of brass or other metal materials that can withstand internal temperatures such as, for example, 1800.degree. F. or more.